This invention relates to an on-board inert gas generation system. Specifically, the invention relates to a method and apparatus for increasing the pressurized air provided to an air separation module of the system.
On-board inert gas generation systems are increasingly used in aircraft to provide inert gas to various locations such as the cargo area or fuel tanks. Typically, the system includes two compressors or stages arranged in series for providing compressed air to the air separation module. It is desirable to provide high pressures to the air separation module to reduce the weight of the module. Lowering the inlet pressure to the module greatly increases its weight.
Centrifugal compressors are typically used in the system to provide compressed air to the module. One proposed system employs an electric motor to drive the compressors. The electric motor does not utilize all the available electric power to drive the compressor because of compressor rotor blade design limitations. Although more electrical power is available, it is not used to drive the compressor at higher speed to increase pressure to the module. Specifically, in order to increase the compressor pressure ratio and provide increased pressure to the module inlet for a given flow rate and fixed motor speed, the rotor blade height must be decreased. Because the gap height between the blade and compressor housing is essentially fixed, decreasing the rotor blade height decreases the ratio of rotor blade height to gap height, which causes the efficiency of the compressor to drop to an unknown and unpredictable level, thereby compromising the integrity of the system.
It is desirable in the industry to utilize rotor blade designs that have been proven in previous commercial applications. This lowers the risk to the customer and increases confidence that the compressor will perform as predicted while reducing system lead times and development costs.
What is needed is an on-board inert gas generation system that utilizes proven centrifugal pump rotor designs while providing increased inlet pressure to the air separation module.